The only one of these I'm seeing is that there's no right-click menu for conversations in the desktop client, which does slightly violate my expectations. As to everything else:

Signal desktop takes 4 seconds to launch for me. That's a bit slow, but I launch it at boot and leave it open all the time.

I see a ... menu when I hover over messages in a chat; its contents are identical to what I see right-clicking the message.

Copy/paste of images into and out of chats works for me. The voice clip button works for me.

I'd be annoyed if I ran into a bunch of client bugs like these too, but they do sound like bugs rather than bad design. If you haven't used it in a while, they may be fixed.